TrueNAS 4x 12TB RAID 5 NAS Calculator

Estimate usable TB, parity, and fault tolerance for TrueNAS NAS users using 4x 12TB in RAID 5.

Planning route

Answer the capacity question, then validate the purchase path

Use this worked example as a numeric starting point, then validate the RAID choice, capacity reserve, hardware plan, and backup path.

Decision aid RAID level selector Reference Capacity matrix

Editorial method

Turn the result into a storage brief

The capacity model makes drive count, drive size, RAID layout, and reserve visible. Use the resulting brief to check exact performance, rebuild duration, hardware compatibility, and the recovery plan for the chosen system.

Last reviewed: July 10, 2026. Product links remain neutral category searches until a partner relationship and page-level disclosure are in place.

OpenZFS checksums and scrubs Background on checksum verification, scrubs, and repair in suitably redundant ZFS pools. Read primary source ↗ TrueNAS data protection Official overview of scrubs, S.M.A.R.T. tests, snapshots, replication, and backup tasks. Read primary source ↗ CISA ransomware guidance Why recoverable, regularly tested backups should be separate from array redundancy. Read primary source ↗

Capacity Snapshot

Raw Capacity

48.00 TB

Usable Capacity

32.40 TB

Fault Tolerance

1 drive

Efficiency

75.0%

Balanced capacity and redundancy, but rebuild stress can be high on large disks. This scenario applies a 10% filesystem reserve.

Run Interactive Calculator →

Alternative Mode Comparison

Mode	Usable	Tolerance	Efficiency
RAID 5	32.40 TB	1 drive	75.0%
RAID 6	21.60 TB	2 drives	50.0%
RAID 10	21.60 TB	1 drive per mirror pair*	50.0%
RAID-Z1	32.40 TB	1 drive	75.0%
RAID-Z2	21.60 TB	2 drives	50.0%

TrueNAS / ZFS Planning Notes

TrueNAS and ZFS planners usually care about parity width, scrub cadence, and healthy operating headroom. Capacity is only one part of pool durability.

• Treat RAID-Z2 as a common baseline for medium and large homelab pools.
• Keep meaningful free space to reduce fragmentation pressure under snapshots.
• Plan vdev growth strategy early, since expansion paths affect long-term efficiency.

Brand / Region Glossary

vdev

A virtual device group in ZFS; multiple vdevs form a storage pool.

Scrub

Background integrity scan that verifies checksums and repairs parity mismatches.

RAID-Z Expansion

ZFS feature set and planning topic for growing parity groups safely.

NAS cluster navigation

Move through the storage decision path

All apps

NAS Hub Calculator and buying path Learning Center 8-step guide path RAID Comparison Mode-by-mode matrix RAID Selector Choose by priority Capacity Matrix Citation-ready reference NAS FAQ Planning answers

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Sequential long-tail navigation

← Previous: QNAP 4x 12TB RAID 5 NAS Calculator Next: Unraid 4x 12TB RAID 5 NAS Calculator →

FAQ

How much real-world usable storage does 4x 12TB RAID 5 provide?

For TrueNAS users, this NAS planning scenario estimates 32.40 TB usable after a 10% reserve from 48.00 TB raw.

Should I optimize this 4-drive plan for capacity or resiliency first?

For long-lived NAS pools, resiliency first is usually safer. Capacity can be expanded later, while a risky parity choice can force migration sooner.

How many disk failures can RAID 5 tolerate in this setup?

This setup can tolerate 1 drive. Real-world survivability depends on mirror placement, rebuild stress, and drive health.

Can this calculator replace real-world benchmark and rebuild testing?

No. Use this page for pre-purchase sizing, then validate with workload benchmarks, SMART health policy, and a tested restore plan.